CADAVERIC CHANGES IN THE MUSCLES 127 in the pelvis. Post-mortem staining does not occur in the heart, but it may contain the so-called " cardiac polypi " which are post-mortem fibrinous clots. Hypostasis in internal organs, such as the brain, lungs, stomach? kidneys and intestines, has to be distinguished from congestion or inflammation of those organs. Difference between Post-mortem Staining and Congestion in an Organ,— Post-rnortem staining in an organ is irregular, and occurs on a dependent part; redness caused by congestion is generally uniform and all over the organ. The mucous membrane in post-mortem staining is dull and lustre- less, but not so in congestion. In post-mortem staining inflammatory exudation will not be seen, and areas of redness alternating with pale areas will be found if a hollow viscus is stretched out and held in front of light. 6. CADAVERIC CHANGES IN THE MUSCLES After death the muscular tissues of the body pass through three stages : (1) Primary relaxation or flaccidity, (2) Cadaveric rigidity or rigor mortis, (3) Secondary relaxation. (1) Primary Relaxation or Flaccidity*—Soorx after death the whole muscular system commences to relax except in those cases where the muscles have been in a contracted condition before death ; hence we notice that the lower jaw of a dead body falls, the eyelids lose their tension, the extremities become soft and flabby, and the joints are flexible. But the _rnuscles are contractile, and react to*external stimuli, mechanical or electrical, owing to their retaining molecular life after somatic death. This stage lasts from three to six hours, but the average is two or three hours. One hour and fifty-one minutes is the average period of duration in Bengal as found by Mackenzie.13 (2) Cadaveric Rigidity or Rigor Mortis.—This phenomenon, which is also known as death stiffening, comes on immediately after the muscles have lost the power of contractility, and affects all the muscles of the body, both voluntary and involuntary. A satisfactory theory has not yet been advanced to explain the chemical changes which occur in the muscle tissues during the process of rigor mortis, but Szent-Gyorgyi and others 14 have shown from their recent investigations that adenosine triphosphate (ATP) plays a fundamental role not only in the normal contraction and relaxation of living muscles, but in determining the physical condition of the muscle proteins. According to them the muscle protein which was formerly known as myosin consists of a combination of two proteins, viz. myosin and actin. The combined form, is called actomyosin, and possesses the property of contractility and relaxation in the presence of adenosine triphosphate which is normally closely bound to the muscle proteins. They have further proved that the presence of adenosine triphospliate absorbed in the muscle proteins is essential for the preservation of the normal degree of hydration, which is concerned in maintaining the suppleness of living muscle. After death, the adenosine triphosphate is decomposed pro- gressively and disappears from the muscles, and thus causes dehydration which results in rigor mortis. During rigor mortis the reaction of the muscle changes from slightly alkaline to distinctly acid, due probably to the formation of lactic acid during the process of the breaking down of the muscle proteins. 13. Jnd. Med. Gaz., June 1889, p. 167. 14. Sydney Smith and F. S. Fiddles, Forens. Med., Ed. IX, p. 21.